Conventional technologies for measuring motions of human bodies or the like are classified into a method of installing a sensor in a place away from a measuring target to measure it (method by remote measurement), and a method of attaching a sensor to a measuring target itself to measure its motion without relying on a signal or the like from the outside (method by autonomous measurement).
As the method by the remote measurement, there are a method of using an optical image sensor (e.g., JP2000-182058A, JP2002-8043 A, or JP 10-74249 A), a method of using a magnetic sensor, and the like.
As the method by the remote measurement can execute measurement only in a space in which the sensor installed outside is functional, its measuring range is limited. Depending on a sensor type, there is a space in which the sensor cannot be installed. For example, a method of tracking by the optical image sensor with an LED or the like as a mark cannot be used outdoors when it is bright. A method of tracking a marker attached to a measuring target by applying an infrared light (e.g., VICON by Vicon Motion Systems Inc.) cannot be used outside, either. In the case of using a magnetic sensor (e.g., Motion Star ASCENSION Inc.), measurement is impossible in a magnetically fluctuating environment.
On the other hand, the method by the autonomous measurement has an advantage of no restrictions on a measuring range. Measuring methods are so-called mechanical types to measure elongation/contraction of a wire, a change in an angle of a bar, relative distances among sensors attached to four limbs, or the like (e.g., by Gypsy Spice Inc.), and they are similar in that joint angles are measured.
All the methods need to attach the sensor to each limb, restricting a joint motion itself in many cases. As the sensor itself is large, its appearance gives an uncomfortable feeling, and thus the sensor is not suitable for outdoor use. Accuracy of angle measurement is low, and thus unsatisfactory for highly accurate operation measurement.
Incidentally, a recent progress made in semiconductor microfabrication technology has made available an acceleration sensor and an angular velocity sensor called MEMS inertia sensors at reasonable prices. A compact inertia measuring instrument constituted of such a MEMS inertia sensor is inferior in accuracy to a conventional inertia navigation instrument or gyro used for posture control of an aircraft or the like. However, it has a compact and light-weight feature.
Thus, it is not impossible now to attach the sensor to the body thereby measuring a human posture. However, to calculate a moving distance or a direction from an output of the inertia sensor, integration must be carried out twice in the case of the acceleration sensor, and once in the case of the angular velocity sensor. Accordingly, small errors accumulate with time caused by a fluctuation in a still output which accompanies electric noise in the sensor output, a shift in gravity axis, or a change in a surrounding environment such as a temperature. A drift phenomenon occurs in a measuring position even in a still state. As a method of correcting this drift, use of an external signal of an ultrasonic wave, magnetism, a light, or the like is general. For example, in motion tracking (refer to U.S. Pat. Nos. 6,176,837 and 6,474,159), an instrument for determining a direction or a position of a body, or a head mount display instrument for reproducing a human posture in a virtual space of a computer is realized by a system for correcting an error of an inertia measuring instrument by an ultrasonic wave. However, those methods impose spatial restrictions after all as in the case of the aforementioned method by the remote measurement. An attempt has been made to measure a joint angle of a human body only by an inertia sensor (refer to JP 11-325881 A). However, there are restrictions in that the sensor must be attached as close as possible to both ends of the joint, and usable places are limited to a hand, a leg, and the like.
Measurement of a motion of a human body is necessary in many fields. In management engineering, there is an example of measuring and analyzing a working motion of a worker in detail to improve working efficiency. In computer graphics, to represent a real human motion, the human motion must be accurately measured. In a medical field, measurement of a motion must be accurately carried out to quantitatively understand how a motion of a patient is improved in a process of rehabilitation or the like. Thus, the human body motion measuring system is expected to be used for various purposes, and some measuring systems have been developed. However, in measurement, most of the systems inevitably impose restrictions on human behaviors which become measuring targets. Besides, the number of systems in which measuring costs are high is not small.
With the foregoing in mind, the present invention proposes a system which can correct the aforementioned drift phenomenon of the measuring position and execute efficient measurement with restrictions as small as possible on contents or places of motion (e.g., not only indoor but also outdoor free spaces) regarding a human to be measured.